The invention relates to an apparatus for suppressing body noise also referred to as structure borne noise, for example in a carrier structure that connects a noise source to a structural component such as an enclosure for example the cell of a helicopter.
It is known, for example in connection with the mounting of a helicopter power plant to the helicopter cell by connector struts to suppress body noise by an active reduction in the body noise transmission. Such active reduction is accomplished by counteracting or compensating body noise caused by primary loads by counterforces and moments in the form of secondary loads which are controlled in closed loop fashion. Such compensation, is for example realized by means of magnetostrictive or piezoelectric actuators in connection with a respective inertia mass which introduce the required counterforces or moments into the carrier or connector struts.
The actuators are conventionally secured to a first end of the mounting strut or carrier structure and preferably in the longitudinal direction of the strut or carrier structure. An inertia mass is secured to the opposite or second end of the strut or carrier structure. The actuators move the inertia masses secured to the strut or carrier structure in response to the movements of the struts or carrier structure, thereby causing a superposition of two motions or vibrations, namely the motion of the inertia masses motion at the foot of the strut or carrier structure is superposed on the motion of the strut or carrier structure in such a way that the two motions cancel each other at least partially, whereby body noise is suppressed. This superposition of motions or vibrations takes place in the frequency range of the body noise. Therefore, the conventional devices are capable of at least partially suppressing the transmission of body noise from the power plant to the helicopter cell.
The relatively large weight of the above described conventional noise damping structure is a disadvantage, especially an aircraft such as helicopter structures. The weight includes the actuators and the inertia masses as well as the spatial integration of the structure into the strut or carrier structure. Another disadvantage of the above conventional construction is seen in that the combination of actuators with inertial masses has been found to be wanting with regard to achieving the intended noise reduction to a desirable extent. Thus, there is room for improvement.
In view of the above it is the aim of the invention to achieve the following objects singly or in combination:
to provide a device for the suppression of body noise more efficiently than was possible heretofore, while substantially reducing the weight of such body noise suppression devices;
to suppress or even eliminate the transmission of noise caused by noise source vibrations and oscillations, through a connector strut or carrier structure from the noise source, such as the main power plant, to an enclosure, such as a helicopter cell or other structural components, such as a vehicle body, while achieving the suppression or elimination in a simple construction that is easily integrated into a connector strut or carrier structure;
to completely avoid the use of additional inertia masses by using system masses for the body noise compensation, particularly the mass of the main power plant of a helicopter; and
to control the excitation of piezoactuators in closed loop fashion for the noise suppression or noise isolation of the enclosure from the higher frequency noise generation of a power plant including a power transmission.
The piezoactuator is integrated into or bonded to the connector, for example by a suitable adhesive, whereby the piezoactuators elements are preferably piezoelectric elements that can be excited by a controlled power source which in turn is controlled in closed loop fashion so that the actuators cause a blocking of the body noise transmission in the longitudinal direction of the struts as well as in the transversal direction and even in the torsion direction around the struts or connectors. According to the invention the body noise compensation or suppression is accomplished by using system inertia masses, e.g. the power plant mass, particularly in a helicopter.
It is an advantage of the invention that the piezoelectric actuators are directly applied, for example by adhesives to the connectors without the use of any additional inertia components. More specifically, the attachment of inertia masses to one end of the connectors is altogether avoided according to the invention, whereby the manufacturing costs of the body noise suppression devices according to the invention are substantially reduced, compared to the above described prior art. Another advantage of the invention is seen in that the application or integration of the piezoactuators in or to the connectors is simple and the weight of these actuators is substantially smaller compared to conventional structures that require additional mass for the noise suppression. Moreover, these piezoelectric actuators require but little space. As a result, the body noise suppression devices according to the invention are especially suitable for lightweight structures. Yet another advantage of the invention is seen in the substantially improved effectiveness in the noise reduction or suppression as compared to the above prior art.
In a preferred embodiment several piezoactuator layers or strips are applied to the connector and each of these layers or strips may be individually controlled by its respective power source, whereby countervibrations can be generated for different vibration patterns of the connector. By integrating the piezoactuators as taught herein directly into the mechanical connector between the noise source and an enclosure, in combination with a control program for the excitation of the piezoelectric actuators, it is possible to achieve a noise isolation of the enclosure or structural component from the higher frequency excitations of a respective engine such as a power plant including a transmission.